The GMRT 150 MHz all-sky radio survey

Abstract

We present the first full release of a survey of the 150 MHz radio sky, observed with the Giant Metrewave Radio Telescope (GMRT) between April 2010 and March 2012 as part of the TIFR GMRT Sky Survey (TGSS) project. Aimed at producing a reliable compact source survey, our automated data reduction pipeline efficiently processed more than 2000 h of observations with minimal human interaction. Through application of innovative techniques such as image-based flagging, direction-dependent calibration of ionospheric phase errors, correcting for systematic offsets in antenna pointing, and improving the primary beam model, we created good quality images for over 95 percent of the 5336 pointings. Our data release covers 36 900 deg 2 (or 3.6 π steradians) of the sky between −53• and +90• declination (Dec), which is 90 percent of the total sky. The majority of pointing images have a noise level below 5 mJy beamwith an approximate resolution of 25 × 25 (or 25 × 25 /cos (Dec − 19 • ) for pointings south of 19 • declination). We have produced a catalog of 0.62 Million radio sources derived from an initial, high reliability source extraction at the seven sigma level. For the bulk of the survey, the measured overall astrometric accuracy is better than two arcseconds in right ascension and declination, while the flux density accuracy is estimated at approximately ten percent. Within the scope of the TGSS alternative data release (TGSS ADR) project, the source catalog, as well as 5336 mosaic images (5• × 5 • ) and an image cutout service, are made publicly available at the CDS as a service to the astronomical community. Next to enabling a wide range of different scientific investigations, we anticipate that these survey products will provide a solid reference for various new low-frequency radio aperture array telescopes (LOFAR, LWA, MWA, SKA-low), and can play an important role in characterizing the epoch-of-reionisation (EoR) foreground. The TGSS ADR project aims at continuously improving the quality of the survey data products. Near-future improvements include replacement of bright source snapshot images with archival targeted observations, using new observations to fill the holes in sky coverage and replace very poor quality observational data, and an improved flux calibration strategy for less severely affected observational data.

Radio spectra of bright compact sources at z>4.5

“…In project 21 013, sources were only considered for observation if they had steep radio spectra (α < −0.5) based on their VLBI flux densities. To ensure that the sources were sufficiently bright to be detected with the GMRT, in project 29 007, we selected sources based on their 1.4 GHz flux densities in FIRST, and based on whether they were detected at 325 or 148 MHz with the Westerbork Northern Sky Survey (WENSS; Rengelink et al 1997) The data were reduced using the SPAM pipeline as described by Intema et al (2016). The flux density scale was set by 3C48, 3C147 or 3C286 and was tied to the Scaife & Heald (2012) standard with an accuracy of ∼ 10 per cent (e.g.…”

Radio Counterparts of Compact Binary Mergers Detectable in Gravitational Waves: A Simulation for an Optimized Survey

“…We also consider the detectability at 150 MHz with the LOFAR (van Haarlem et al 2013). Note that, apart from these telescopes, there are other relevant telescopes including: WSRT/Apertif (Oosterloo et al 2010), GMRT (Intema et al 2016), and MWA (Tingay et al 2013). Note that the values of the JVLA are based on current data while the other values are based on current predictions of performance.…”

Searching for pulsars associated with the Fermi GeV excess

“…We generated our initial candidate list from a recently published continuum all-sky survey carried out on the Giant Metrewave Radio Telescope (GMRT) at a frequency of 150 MHz (TGSS ADR; Intema et al 2016). Pulsars stand out at 150 MHz.…”

“…As we are interested only in point sources and not extended sources (HII regions, supernova remnants, extragalactic sources, etc. ), it would be standard practice to apply a cutoff based on the ratio of the total flux (St) to peak flux density (Sp) following Intema et al (2016). However, this approach would likely eliminate real point sources due to the known enhanced scattering over large regions toward the galactic center (e.g.…”

“…Navarro et al 1995;Broderick et al 2016;Frail et al 2016a). In this paper we carry out a pilot study, using the recently published GMRT 150 MHz all-sky survey (TGSS ADR; Intema et al 2016) and existing images at higher frequencies to search for compact, steep spectrum radio sources within the central 2.5 • radius of the gamma-ray excess. In §2 we describe our candidate selection method, §3 summarizes our observations of two candidates, data processing, and results, and §4 presents conclusions.…”